1. Field of the Invention
The present invention relates to a method of upgrading an optical node, and an optical node apparatus, in an optical communication system for transmitting a wavelength division multiplexed (WDM) signal light. In particular, the present invention relates to a method of upgrading an optical amplification repeating node to an optical add/drop multiplexing (OADM) node, and an optical node apparatus.
2. Description of the Related Art
Currently, in the metro-core ring, a system for acquiring signal lights of the number of wavelengths (channels) corresponding to a required communication traffic is applied to an OADM node arranged in each metropolitan area, using a WDM transmission system. In a part of the area where such an OADM node is arranged, there is the case where the communications needs have been zero in the beginning of the system construction, but due to the area development thereafter or the location of data center, the communications needs are rapidly increased.
As a method of upgrading the system for coping with the increase of communications needs as described above, there is, for example, a method of installing an optical node apparatus having an OADM function in such an area from the beginning, to enable the OADM function when the communications needs occur (refer to Japanese Unexamined Patent Publication No. 2004-297235). Further, it is also possible to initially install an inline amplifier as an optical amplification repeating node which does not have the OADM function, and to replace the inline amplifier with the optical node apparatus having the OADM function when the communications needs occur, thereby upgrading an optical node from the optical amplification repeating node to the OADM node.
However, in the conventional upgrading method of installing the optical node apparatus having the OADM function from the beginning as described above, there is a problem in that the initial installation cost becomes expensive. Further, in the upgrading method of replacing the inline amplifier initially installed with the optical node apparatus having the OADM function when the communications needs occur, since the communication service in the entire system needs to be suspended for a fixed time when performing the replacement of the optical node apparatus, there is a problem in that the continued communication service cannot be provided.
Moreover, regardless of whether or not the optical node apparatus having the OADM function is installed from the beginning, in the case where an operational state of the optical node apparatus is switched from the optical amplification repeating node to the OADM node according to the communications needs, how quick an operation of the OADM node apparatus after switched can be adjusted to be in an optimum status corresponding to operational channels before switched is a major problem for stably providing the continued communication service.